1. Technical Field
This invention relates to the field of electric fence monitoring systems, and particularly relates to electric fence monitoring systems for detecting and localizing a break in an electric fence.
2. Description of the Prior Art
The use of electric fences for the retention of animals has been known for many years. Electric fences utilize a fence energizer to generate high-voltage electrical pulses which are propagated down one or more conducting wires of the electric fence. When an animal touches a conducting wire, a path to ground is created through the animal. A portion of the electrical pulses pass through the animal to ground and quickly attracts the animal's attention. Advantageously, electrical fences, unlike conventional fences, do not need to strong enough to withstand an animals attempts to push through it. This advantage allows electric fences to be designed and constructed more simply than conventional fences. As a result, less materials may be required and less maintenance may need to be performed than would be required for a conventional fence. This may often result in a significant cost savings over conventional fences. Thus, electric fences are favored by many landowners and have become increasingly popular.
Unfortunately, if an electric fence does break, a significant portion of the length of the fence may be de-electrified. This renders the entire de-electrified portion of electric fence, which is not designed to withstand the force of an animal pushing against it, virtually useless. Thus, an electric fence must be monitored closely and a fence break must be fixed repaired as soon as possible.
The most straightforward method of monitoring an electric fence is to manually inspect the electric fence on a regular basis to verify that it is in working order. However, many electric fences are installed over rough terrain or over-grown areas which make it difficult to access portions of the fence for inspection. Moreover, the length of electric fences may extend thousands of feet or even miles, making the process of inspecting each point on such a fence exceedingly time-consuming. Thus, a need exists for a monitoring system which automatically alerts a user to a failure in an electric fence without requiring him to perform a manual inspection of the fence.
One technique employed by a prior art system, uses a monitoring device consisting of a voltage and current sensing devices, which are located in close proximity to the fence energizer, to monitor the electrical activity on the fence. If the voltage reading falls out of a specified range or the current reading falls rapidly, the sensing devices trigger an alarm. This technique attempts to simulate conditions at the far end of the electric fence by adjusting the readings based on the length of the fence. Unfortunately, the accuracy, flexibility and dependability of this system suffer because there are no sensing devices located at remote points of the electric fence. Further, such a system requires that the monitoring device be tuned to ensure that the system works accurately when the system is installed or modified.
Another technique is to position a transponder at the far end of an electric fence to: (a) receive the high-voltage electrical pulses which are propagating through the conducting wire; (b) generate a return pulse; and (c) transmit the return pulse back over the conducting wire to a digital analyzer located adjacent to the energizer. Unfortunately, this technique is only able to monitor a single location. This makes it difficult to localize the condition causing the actual problem. In addition, the transponder sends and receives the electrical pulses through the conducting wire of the fence, which is a relatively unreliable medium.
Another technique is to use a single receiver/monitor located in close proximity to the energizer, and multiple responders. Separate responders are placed at each branch of an electric fence. This technique allows each branch of the fence to be monitored simultaneously. Each responder receives the high-voltage electrical pulses over the conducting wire and periodically generates a return pulse based on conditions associated with the received pulses. Each responder delays a specific amount of time before transmitting its return pulse over the conducting wire to the receiver/monitor. Using separate circuits for each responder, the receiver/monitor discriminates between the various return pulses by the amount of time that elapses between the energizer pulses and the responder return pulses. Thus, changes in electrical conditions in a particular branch of the electric fence will effect the generation of the corresponding responder's return pulse, and delays in the generation of that return pulse are detected by the receiver/monitor. This technique allows the receiver/monitor to isolate a problem to a particular branch; however, the fence must be manually inspected to pin point the source of the problem. Further, the number of responders which may be used in this technique is limited by the size of the receiver/monitor because separate circuits are required for each additional responder. In addition, as the number of responders increases and the complexity of the fence system increases, the use of signaling techniques utilizing only the conductor wire of the electric fence becomes less and less workable, as multiple signals generated by additional responders attempt to use the same low quality transmission line over greater and greater distances. Finally, the installation or modification of system employing this technique requires that the responders and the receiver/monitor to be tuned to ensure that the system works accurately.
Thus, a need exists for an electric fence monitoring system that allows the use of multiple remote sensors spread strategically over the entire fence system, the reliability of which is not affected when additional sensors are added, and which may be more easily installed or modified by a user.